Electric machine, especially a generator for motor vehicles

ABSTRACT

An electric machine, particularly a generator for motor vehicles, is indicated, which has a housing ( 10 ) and a casing ( 17 ) enclosing the housing ( 10 ) concentrically, the casing, together with the housing ( 10 ), bounding an annular space ( 18 ) that is sealed in a fluid-tight manner and is connected to a coolant outflow and a coolant inflow. To achieve a uniform circumflow of the housing ( 10 ) with sufficient cooling capacity, even given low volumetric flow of the coolant, a plurality of axial guide bars ( 25 ) are arranged in the annular space ( 18 ), so that the coolant restrictedly flows in an axially wide-strip manner through the annular space ( 187 ) within space segments ( 26 ) arranged in a row in the circumferential direction, with an opposing flow direction in successive space segments ( 26 ).

BACKGROUND INFORMATION

[0001] The present invention is based on an electric machine,particularly a generator for motor vehicles, according to the preambleof claim 1.

[0002] In a known water-cooled generator for motor vehicles (FR 2 717638 A1), the stator and rotor are accommodated in a pot-shaped housingwhich, on one hand, is inserted into a pot-shaped encasing in such a waythat an annular space remains between the covering of the pot-shapedencasing and the outer surface of the housing, the annular space beingcovered in a fluid-tight manner on one side by the bottom of theencasing, and on the other side, by a cover mounted on the pot edge ofthe encasing and housing. The annular space, on sides turned away fromeach other, has an inflow orifice and a discharge orifice which are eachenclosed by a connecting piece, projecting radially on the encasing, fora water pipe. The water circulated by a pump in a circulation circuitenters into the annular space through the inflow orifice, circumflowsthe housing, and exits the annular space again via the dischargeorifice. The heat emitted by the generator is absorbed by the coolerwater and carried away.

SUMMARY OF THE INVENTION

[0003] The electric machine of the present invention has the advantagethat, because of the forced guidance of the coolant by the guide bars, auniform circumflow of the housing of the electric machine by the coolantis ensured, so that—unlike in the related art—the formation of so-called“hot spots” because of locally insufficient flow velocity of thecoolant, for example, due to the development of recirculation bubbles,is prevented. Because of the multitude of guide bars, which at the sametime act as cooling vanes, the housing surface available for heattransfer to the coolant increases, so that for an equal coolingcapacity, the volumetric flow of the coolant may be reduced by thefactor by which the housing surface is increased. Due to the wide-stripaxial flow of the coolant, which in each case is turned around at theend sides of the annular space, at the location where the stator of themachine supplies a large input of heat through the metallic housing, thesurface for the heat transfer and the flow velocity of the coolant arealso great, so that the local cooling capacity is well adapted to thelocal heat input. If desired, the spacings of the guide bars may bedimensioned accordingly for this purpose, as well. Short-circuit lossesdue to leakage currents over the guide bars are low, since because ofthe configuration which is favorable for the flow, no large pressuredifferences result across the small gaps present between the coveringand the outer surface of the guide bars.

[0004] All in all, in the machine of the present invention, sufficientlygreat cooling capacity is furnished for heat dissipation in all spacesegments, and indeed also for the cases when only a limited volumetricflow of the coolant is available.

[0005] The measures specified in the further claims permit advantageousfurther developments and improvements of the electric machine indicatedin claim 1.

[0006] According to one preferred specific embodiment of the invention,the guide bars in each space segment form a plurality of parallel flowchannels having in each case an inflow end and an outflow end. In theannular space, at each end of the flow channels, coolant collectingsections are formed, extending in the circumferential direction, ofwhich in each case one inflow collecting section extends over the inflowends and one outflow collecting section extends over the outflow ends ofeach space segment. At each end of the flow channels, adjoining thedischarge collecting section of the one space segment in thecircumferential direction is an inlet collecting section of thefollowing space segment, each inlet collecting section being separatedfrom the discharge collecting section of the space segment following inthe flow direction. This parallel arrangement of the guide bars in afew, e.g. five, space segments distributed over the periphery of thehousing reduces the length of the cooling channel and the resistance toflow.

[0007] According to one advantageous specific embodiment of theinvention, the coolant collecting sections are formed in such a way thatthe cross-section of the inlet collecting sections decreases in the flowdirection, and the cross-section of the discharge collecting sectionsincreases in the flow direction. Due to this structural formation, theflow velocity in the region of the re-routing of the coolant flow isreduced, and coolant is uniformly distributed to the parallel flowchannels, accompanied by uniform flow velocity in the flow channels.

[0008] In one advantageous specific embodiment of the invention, thecoolant collecting sections at the ends of the flow channels are formedin the manner that the guide bars have an equal length, and that withina space segment, successive guide bars in the circumferential directionare shifted axially preferably by equal amounts—in the same directionrelatively to each other. In so doing, the last guide bar in the spacesegment is shifted so far that it is brought forward with one bar end toone of two annular bars terminating the annular space at the end face.Due to this structural design, the desired decrease and increase ofcross-section in the coolant collecting sections and the separation ofthe inflow collecting sections from the outflow collecting sections inthe following space segment are advantageously implemented from thestandpoint of production engineering.

[0009] According to one advantageous specific embodiment of theinvention, an inflow channel extending in the axial direction andconnected to the coolant inflow, and an outflow channel extending in thecircumferential direction and connected to the coolant outflow areformed between the first guide bar of the first space segment in theflow direction and the last guide bar of the last space segment. Theinflow and outflow channels are separated from each other by aseparating bar extending in the circumferential direction from the frontend of the last guide bar in the last space segment up to the firstguide bar in the first space segment. In this context, an inflowconnecting piece for the coolant inflow mounted on the casing is alignedwith its axis in such a way that the axis forms an obtuse angle with theaxial flow direction of the coolant in the inflow channel, and anoutflow connecting piece for the coolant outlet mounted on the casing isimplemented so that its axis forms an obtuse angle with the more or lesstangential flow direction in the outflow channel. Due to this guidanceof the inflow and outflow of the coolant, the pressure at the separatingbar is reduced on the high-pressure side by the volumetric flow directedaway from the separating bar. On the low-pressure side, the pressure atthe separating bar is increased by the dynamic pressure of the upwardlydischarging coolant. All in all, the result thereby on one hand is areduction of the total pressure over the separating bar, so that onlyextremely low leakage losses occur, and on the other hand, a feed anddischarge of the coolant which is favorable to the flow, thus helping toreduce the flow resistance.

[0010] According to one advantageous specific embodiment of theinvention, the guide bars, one annular bar and the separating bar areintegrally molded on the housing, which is produced using pressurediecasting or injection molding techniques. Due to the bar formation,which is selected to be favorable from a standpoint of productionengineering, the pressure or injection mold is able to be drawn off inthe axial direction. The casing, produced separately with integrallymolded annular bar, is slid onto the housing thus produced, and theannular space is sealed by two O-rings between the housing and thecasing in the region of the annular bars.

BRIEF DESCRIPTION OF THE DRAWING

[0011] The invention is explained in detail in the following descriptionin light of an exemplary embodiment shown in the Drawing, in which:

[0012]FIG. 1 shows a longitudinal section of a generator for motorvehicles in a cutaway view;

[0013]FIG. 2 shows a perspective view of the generator in the directionof arrow II in FIG. 1 in a cutaway view;

[0014]FIG. 3 shows a plan view of the generator in FIG. 1, with thecasing drawn off, in a perspective representation;

[0015]FIG. 4 shows a developed view of the housing of the machine inFIGS. 1-3.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0016] The generator, shown in longitudinal section in a cutaway view inFIG. 1, for a motor vehicle as an exemplary embodiment for a generalelectric machine has, as known, a stator 11, accommodated in a housing10, having a stator winding 12, and a rotor 14, enclosed concentricallyby stator 11 leaving an air gap 13, which sits in a rotationally fixedmanner on a rotor shaft 15 rotationally mounted in housing 10. Housing10 is pot-shaped, having a base part 101 and a cylindrical part 102. Oncylindrical part 102, at the end facing away from base part 101, aradial flange 103 is integrally formed, upon which a bearing cover 16 issecured, sealing housing 10 at the front end. Rotor shaft 15—as notshown in FIG. 1—is in each case accommodated in a pivot bearingintegrated in base part 101 and in bearing cover 16.

[0017] Directly adjacent to flange 103, an annular bar 104 is integrallymolded, projecting radially from the surface of cylindrical part 102.From the other end of cylindrical part 102, a separately manufactured,hollow-cylindrical casing 17 is slid onto housing 10 and, with its frontend in the push-in direction, overreaches annular bar 104 on one side,and abuts against flange 103 on the other side. At the rear end ofcasing 17, a radially inwardly projecting annular bar 171 is integrallyformed, whose radial height corresponds to the radial height of annularbar 104 on housing 10. In this way, an annular space 18 is boundedbetween casing 17 and cylindrical part 102 of housing 10 and is sealedat the end faces by the two annular bars 104 and 171. In the region ofannular bars 104 and 171, in each case a ring seal 19 in the form of anO-ring is disposed between casing 17 and cylindrical part 102 of housing10, in each instance a ring seal 19 preferably fitting in an annulargroove 20 cut into cylindrical part 102 of housing 10. Annular space 18is connected to a coolant inflow 21 and a coolant outflow 22, which areeach assigned an inflow connecting piece 23 and outflow connecting piece24, respectively, arranged outside on casing 17.

[0018] To ensure a uniform circumflow of the housing by the coolant, arestricted guidance of the coolant is implemented in annular space 18from coolant inflow 21 to coolant outflow 22. In this context, thecoolant is restrictedly guided by a plurality of axial guide bars 25, sothat it flows in an axially wide-strip manner through annular space 18within segments of the annular space 18 that are arranged in a row inthe circumferential direction, hereinafter known as space segments 26,with opposing flow direction in successive space segments 26. Guide bars25 have a radial bar height corresponding to the radial width of annularspace 18, and in the exemplary embodiment, having the same cross-sectionand same axial length, are arranged parallel and equidistant to eachother, as can be seen in FIGS. 3 and 4. In the exemplary embodimentdescribed here, guide bars 25 are divided over a total of five spacesegments 26; however, the number of space segments 26 may be selected asdesired. In each space segment 26, guide bars 25 form between themselvesa plurality of parallel flow channels 27 having an inlet end 271 and adischarge end 272, which have an equal flow cross-section.Alternatively, guide bars 25 may also be designed and arranged in such away, for example, with differently sized distances between them, thatflow channels 27 enclosed by them have different flow cross-sections. Inthis context, the different flow cross-sections are spatially allocatedin adaptation to locally different heat input into housing 10. Withineach space segment 26, inlet ends 271 lead into an inlet collectingsection 28 and discharge ends 272 lead into a discharge collectingsection 29, so that at each end of flow channels 27, adjoining in eachcase a discharge collecting section 29 of the one space segment 26 inthe circumferential direction is an inlet collecting section 28 of thefollowing or preceding space segment 26. In inlet collecting sections 28and discharge collecting sections 29, known altogether as coolantcollecting sections, the coolant is distributed to individual flowchannels 27 in space segment 26, i.e. the coolant emerging from flowchannels 27 is combined and turned around in its flow direction. Toavoid short-circuit currents or leakage currents from inlet collectingsection 28 of the one space segment 26 to discharge collecting section29 of space segment 26 following in the flow direction, in each caseinlet collecting section 28 of the one space segment 26 is separatedfrom discharge collecting section 29 of space segment 26 following inthe flow direction. As FIGS. 3 and 4 show, coolant collecting sections28, 29 are designed in such a way that each cross-section of inletcollecting sections 28 decreases in the flow direction, and eachcross-section of discharge collecting sections 29 increases in the flowdirection. The coolant collecting sections with their cross-sectionschanging in the flow direction are realized in the manner that parallelguide bars 25 following one another in the circumferential directionwithin a space segment 26 are shifted axially by an amount, preferablyby the same amount in each case, in the same direction relative to eachother. In so doing, the last guide bar 25 in each space segment 26 isshifted so far that with one of its two bar ends, it abuts against oneof annular bars 104 and 171, respectively, and consequently separatesinlet collection section 28 from discharge collecting section 29 ofspace segment 26 following in the flow direction.

[0019] As can be seen in FIGS. 3 and 4, between first guide bar 251 offirst space segment 261 in the flow direction and last guide bar 252 oflast space segment 262 in the flow direction, an inflow channel 30 isformed that is connected to coolant inflow 21 and extends in the axialdirection, and an outflow channel 31 is formed that is connected tocoolant outflow 22 and extends in the circumferential direction. Inflowchannel 30 and outflow channel 31 are separated from each other by aseparating bar 32 extending in the circumferential direction from thefront end of last guide bar 252 in last space segment 262, up to firstguide bar 251 in first space segment 261. To reduce the total pressureprevailing at separating bar 32, and consequently to avoid possibleleakage losses via the small gap which may form between the bar surfaceof separating bar 32 and the inner surface of casing 17, or to keep theleakage losses very small, inflow connecting piece 23 is formed in sucha way that its axis forms an obtuse angle α with the axial flowdirection of the coolant in inflow channel 30, as is symbolized in FIG.3 by inflow arrow 33 (see also FIG. 2). On the other hand, outflowchannel 31 is formed in such a way that its axis runs more or lesstangentially with respect to housing 10, or in its circumferentialdirection, and likewise forms an obtuse angle β with the flow directionin outflow channel 31, as is symbolized in FIG. 3 by outflow arrow 34(see also FIG. 2).

[0020] The arrangement of guide bars 25 and flow channels 27 formedbetween guide bars 25 can be seen very well in the developed view ofhousing 10 shown in FIG. 4. The flow of the coolant in individual flowchannels 27 and in the coolant collecting sections at flow ends 271 and272 of flow channels 27 is symbolized by the flow arrows drawn in inFIG. 4.

[0021] Housing 10, together with parallel guide bars 25, separating bar32 and annular bar 104, is advantageously produced using the pressurediecasting or injection molding method. Because of the structural designof housing 10, the pressure or injection mold is then able to be drawnoff axially, and after the generator is completed, separately producedcasing 17 may be slid so far onto housing 10 that the front end face ofcasing 17 in the push-in direction strikes against flange 103 formed oncylindrical part 102 of housing 10. Housing 10 and casing 17 are heldtogether by fastening screws 35 which are screwed through flange 103into the end face of casing 17. At the same time, screws 35 also affixbearing cover 16 on flange 103 (FIGS. 1 and 2).

What is claimed is:
 1. An electric machine, particularly a generator formotor vehicles, comprising a housing (10) and a casing (17) whichencloses the housing (10) concentrically and which, together with thehousing (10), bounds an annular space (18) that is sealed in afluid-tight manner and is connected to a coolant inflow (21) and acoolant outflow (22), wherein a plurality of axial guide bars (25) arearranged in the annular space (18) in such a way that the coolantrestrictedly flows in an axially wide-strip manner within space segments(26) arranged in a row in the circumferential direction, with opposingflow direction in successive space segments (26).
 2. The machine asrecited in claim 1, wherein the guide bars (25) have a radial bar heightcorresponding to the radial width of the annular space (18).
 3. Themachine as recited in claim 1 or 2, wherein in each space segment (26),the guide bars (25) form a plurality of parallel flow channels (27)having in each case an inlet end and outlet end (271, 272); in theannular space (18) at each end of the flow channels (27), coolantcollecting sections are formed extending in the circumferentialdirection, of which in each case one inlet collecting section (28)extends over the inlet ends (271) and one discharge collecting section(29) extends over the discharge ends (272) of the flow channels (27) ofeach space segment (26); at each end of the flow channels (27),adjoining the discharge collecting section (29) of the one space segment(26) in the circumferential direction is an inlet collecting section(28) of the following space segment (26); and each inlet collectingsection (28) is separated from the discharge collecting section (29) ofthe space segment (26) following in the flow direction.
 4. The machineas recited in claim 3, wherein the coolant collecting sections areformed in such a way that the cross-section of the inlet collectingsections (28) tapers in the flow direction, and the cross-section of thedischarge collecting sections (29) increases in the flow direction. 5.The machine as recited in claim 4, wherein the cross-sections of theflow channels (27) formed between the guide bars (25) are of equal size.6. The machine as recited in claim 4, wherein the cross-sections of theflow channels (27) formed between the guide bars (25) are dimensionedwith different size in adaptation to the heat dissipation to be carriedout differently locally.
 7. The machine as recited in one of claims 3-6,wherein the coolant collecting sections at the ends of the flow channels(27) are formed in the manner that the guide bars (25) have the samelength, and within a space segment (26), successive guide bars (25) inthe circumferential direction are shifted axially by preferably equalamounts in the same direction relative to each other.
 8. The machine asrecited in claim 7, wherein the last guide bar (25) in the space segment(26) is brought forward with one bar end up to one of two annular bars(104, 171) sealing the annular space (18) at the end face.
 9. Themachine as recited in one of claims 1-8, wherein between the first guidebar (251) of the first space segment (261) in the flow direction and thelast guide bar (252) of the last space segment (262), an inflow channel(30) is formed extending in the axial direction and connected to thecoolant inflow (21), and an outflow channel (31) is formed extending inthe circumferential direction and connected to the coolant outflow (22);and the inflow and outflow channels (30, 31) are separated from eachother by a separating bar (32) extending in the circumferentialdirection from the last guide bar (252) in the last space segment (262)up to the first guide bar (251) in the first space segment (261). 10.The machine as recited in claim 9, wherein the coolant inflow (21) hasan inflow connecting piece (23), mounted on the casing (17), whose axisforms an obtuse angle (α) with the axial flow direction of the coolantin the inflow channel (30).
 11. The machine as recited in claim 9 or 10,wherein the coolant outflow (22) has an outflow connecting piece (31),mounted on the casing (17), whose axis forms an obtuse angle (β) withthe flow direction in the outflow channel (31) pointing in thecircumferential direction of the housing (10).
 12. The machine asrecited in one of claims 8-11, wherein the guide bars (25), theseparating bar (32) and one of the annular bars (104) are integrallymolded on the housing (10).
 13. The machine as recited in one of claims8-12, wherein the casing (17) is produced as a separate component, onwhich the other annular bar (171) is integrally molded; the housing (10)is inserted into the casing (17); and a ring seal (19) is disposedbetween the housing (10) and the casing (17) in the region of theannular bars (104, 171).
 14. The machine as recited in claim 13, whereineach ring seal (19) is inserted in an annular groove (20) introducedinto the housing (10).